High performance airborne radars require extreme suppression of harmonic distortion and spurious responses to avoid false alarms in the presence of ground clutter returns. These requirements impose challenging linearity and spurious response requirements on receiver/exciter designs. Conventionally meeting these requirements through receiver design techniques, such as using high dynamic range components, filtering and isolation, etc., presents a design problem that challenges the state of the art.
Clutter tuning has been used to place clutter returns at a position in the spectrum where interference with the target detection process by harmonics of Mainlobe Clutter (MLC) is minimized. This can be conventionally accomplished with a finely tunable frequency synthesizer which generates an analog modulation used to tune the clutter return signals. The extremely low sideband noise and spurious levels required of the synthesizer itself make the design of the synthesizer challenging and this approach only addresses harmonically generated distortion.
The conventional technique for controlling receiver harmonic distortion involves the use of high dynamic range components and clutter tuning. The conventional technique for controlling receiver spurious responses involves the use of synchronous frequency plans along with filtering and isolation techniques.